Hot water heaters for domestic and other applications include an inner storage tank having an associated heating unit for heating water in the tank. The tank is enclosed with suitable insulation to retain the heat and minimize the necessity for frequent reheating. An outer aesthetically pleasing jacket or shell is provided to enclose the insulation.
A highly satisfactory insulating material is expanded foamed insulation such as expanding foam polyurethane. The insulation is applied in a resinous liquid state into the annular space between the inner storage tank and the outer jacket and foams and expands and hardens to produce a rigid and closely adhering insulating enclosure about the inner tank. For further background, reference is made to U.S. Pat. Nos. 3,521,604 and 4,749,532.
A dam is provided in the annular space between the inner tank and the outer jacket, and prevents leakage of the resinous liquid therepast during the foaming operation. Various types of dams are known in the prior art.
In Clark et al U.S. Pat. No. 4,372,028 a flexible expandable bag 14 is provided around the inner tank in the form of an annular ring or doughnut. After the jacket is installed over the tank, the bag is filled with foam material which expands such that the bag engages the inner surface of the outer jacket and forms a sealing dam Tilton U.S. Pat. No. 4,477,399 shows an inflatable tube 24 providing a dam in the annular space between the inner tank and the outer jacket. Nelson U.S. Pat. No. 4,901,676 shows an annular dam 24 provided by an envelope 26 filled with resilient insulation material 28 and from which air is removed to shrink same and allow the outer jacket to be installed, after which air is allowed back into the envelope such that it expands into abutting contact with both the inner tank and the outer jacket, to provide a sealing dam. Another type of expanding dam is shown in Pfeffer et al U.S. Pat. No. 5,002,709 wherein a band of foamable resin is applied to either the outer surface of the tank or the inner surface of the jacket, which band expands radially to form the dam. In the noted systems, the dam has an initial smaller width to allow the outer jacket to be installed, followed by expansion to a wider width to form the sealing dam.
Pfeffer U.S Pat. No. 4,749,532 shows a layer of fiberglass 15 banded or cinched to the inner tank and forming the dam. A flexible plastic sheet apron 23 is provided over the tank and dam, and protects the fiberglass dam against tearing or snagging as the outer jacket 12 is slid downwardly over the tank. After the jacket is installed, the apron is removed, and the foam insulation is introduced into the annular cavity. Pfeffer U.S. Pat. No. 4,878,482 shows a dam provided by a semi-rigid support element 17 affixed to the inner tank and an outer flexible sealing element 18 in sealing engagement with the outer jacket. Chevalier et al U.S. Pat. No. 4,957,097 shows a dam provided by a flexible strip 19 secured to the outer surface of the inner tank and having an outer lip 22 against which the outer jacket rides while it is being installed. In the assembly methods of Pfeffer '532 and '482 and Chevalier et al, the dam is initially attached to either the inner tank or the outer jacket, followed by installation of the jacket during which the dam is compressed or deflected. It is also known in the prior art to provide an annular resilient compressible pre-formed polymeric sponge-like material dam, e.g., a pre-formed polyurethane foam annular ring or doughnut, around the inner tank, and then installing the jacket, with or without an apron, which jacket slides past and slightly compresses the dam.
It is also known in prior art assembly methods to install the dam after the outer jacket has been installed over the inner storage tank. For example, in Nelson U.S. Pat. No. 4,972,967, the outer jacket 14 is installed over the inner tank 12, after which the dam 22a-22h is pushed downwardly into the annular space between the tank and jacket until stopped against an abutment 50.